Beta-lactamases are serine enzymes that hydrolyze the beta-lactam ring in penicillins and cephalosporins. They are the main cause of penicillin resistance in bacteria. Unlike serine proteases, they do not have a histidine in the active site. Their mechanism of action is not well-understood. We have shown that two lactamases are inhibited (with micromolar Ki's) by several boronic acids. In this study, we will prepare more highly specific boronic acid inhibitors and study their mode of inhibition using enzyme kinetics. The pH-dependence of inhibition is expected to clarify the mechanism of acylation and deacylation. We have studied the effectiveness of boronic acids in inhibiting penicillin resistance and bacterial growth. This will be continued with the new compounds.